The Moon

For die-hard stargazers, Full Moon is the worst time to observe
the sky. A full or nearly full Moon washes out the fainter objects in the
sky, especially deep-sky objects. Even the Moon
itself gives up detail less readily when it is nearly full. The glare is
so intense that looking at the full Moon through a large telescope can
be painful and will temporarily destroy night vision.
Polarizing filters are useful for cutting down on the glare.

For a beginning astronomer with binoculars or a small
telescope, however, the Moon at any phase is the first object to observe.
It is easily found, easily identified, and will show incredible detail
in any optical instrument.

In general, the best time to observe the Moon is when
it is less than half lit, although fuller phases do offer some interesting
views. When the Moon is a crescent, one can often see the outline of the
rest of the lunar disk. This is called "the Old Moon in the New Moon's
arms", or "Earthshine". The latter name refers to the fact that a portion
of the Moon which is not receiving direct sunlight is being dimly lit by
light reflected off the Earth. Thus, we see the dim outline of the full
disk. The line which separates the Moon's brightly sunlit portion from
the rest of the disk is called the terminator. This line divides night
and day on the Moon. On Earth, shadows are long when the Sun is low in
the sky, and the same effect is apparent along the Moon's terminator. Craters
and mountains along the terminator cast long shadows and are thrown into
sharp relief as seen from Earth. The southern portion of the Moon is especially
rich in craters, so this part of the terminator is quite fascinating. When
the Moon is a thin crescent, one can often see a mountain or two poking
up from the unlit portion, catching the Sun's rays while the landscape
around it remains dark.

At Full Moon, there is no terminator. The Moon can be
uncomfortably bright in a telescope when it is near full, although a filter
will cut down on the glare. Several craters are most impressive at Full
Moon, because of their extensive ray systems. The craters Tycho and Copernicus
in particular have a network of white lines extending outward in all directions
from their rims. These rays are ejecta thrown out by the meteorite impacts
that formed the craters.

The Moon offers hundreds of landmarks for amateurs to
explore. Lunar maps and atlases are available at some bookstores and science
stores and from Sky
Publishing.

As mentioned before, some faint astronomical objects are
diminished in appearance when a bright Moon is in the sky. The five brightest
planets, on the other hand, are bright and can
be easily viewed even when the moon is nearby.